To know what happened with Anne Frank, author Ernst Schnabel searched the German and Dutch archives and interviewed survivors of the camps who might have known her.

The diary of 15-year-old Anne Frank ended abruptly when the Nazis broke into her family’s hiding place in Amsterdam. What happened next? Of the last days of one of the world’s best-known modern heroines, little was known except that she had died, like millions of other Jews, in a German…